Mechanical refrigeration



Aug. 30, 1932. H. H. NEsBlTT 1,874,204

' MECHANICAL REFnIGEnA'rIoN x 311e@ June 12. 19:50 Sheets-sheet 1 Harald H. fesbiz ze@ ma E Aug. 30, 1932.

H. H. NEsBlTr' MECHANICAL REFRIGERATION sued June 1,2, 195o s sheets-Shogi?,- -2

3 Sheets-Sheet 5 Aug. 30, 1932. H. H. NEsBlTT MECHANICAL REFRIGERATION Filed June 12. 1930 Jr'gz Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE HAROLD H. NESBITT, 0F BELAIR, MARYLAND, ASSIGNOR TO HARTFORD ENGINEERING AND MACHINE COMPANY, 0F ABERDEEN, MARYLAND, A CORPORATION OF MARY- LAND MECHANICAL REFBIGERATION Application med June 12,'

This invention relates to mechanicalv refrigeration and has for its general object to improve the mechanical as well as the thermal efficiency of mechanical refrigerating apparatus. y

One of the particular objects of the invention is to provide for automatic periodic defrosting of the evaporator element.

Another object of the invention is an improvement in the means for oil separation and the return of oil from the evaporator to the compressor.

A further object of the invention is the construction of an assembly including the evaporator iioat valve, accessible for removal as a unit entirely from the outside of the evaporator.

Other objects of the invention will appear as the following description of preferred and practical embodiments thereof proceed.

In the drawings in which the same characters of reference are used throughout the several figures to denote identical parts;

Figure 1 vis a side elevation of a complete system embodying the principles of the present invention; Figure 2 is a front elevation of the evaporator; y

Figure 3 is a rear view of the same;

Figure 4 is a bottom plan View of the freezing coils;

Figure 5 is a side vertical section of the4 header, showing the valve closed;

Figure 6 is a similar view showing the valve open;

Fi ure 7 is a horizontal section taken along the line 7--7 of Figure 5,;

Figure 8 is a. fragmentary sectional View of a modified Valve control in which a toggle float takes the place of a weighted fioat shown in Figure 1;

Figure 9 is a section taken along vthe line 9-9 of Figure 8; n

Figure 10 is a section taken along the line 10-10 of Figure 8;'` ,y v

Figure 1l is a fragmentary ,view` similar to Figure 8, but showingA Amodified` form of valve; and n y Figure 12 is a side sectional viewV showing the same cam fingers 4which are represented 1930. Serial No. 460,748.

in dotted lines in Fi ure 10, in cooperated relation to an outwar ly opening valve.

Referring now in detail to the several views and first adverting to that form of the invention shown in Figures 1 to 7, inclusive, the system, which is conventional in the relation of its several unitscomprises a compressor 1 driven by a suitable'prime mover such as the electric motor 2, the compressor being interposed in a closed circulation system including the condenser 3 in communication with the discharge end of the compressor, the evaporator 4, which includes the coils 5 and header 6, and the gaseous refrigerant conduit 7 which leads from the evaporator back to the induction side of the compressor.v

It will be understood that liquetiable refrigerant such as sulphur dioxide (SO2) is compressed in the compressor 1, passes as a hot compressed gas through the condenser 3 where it is `cooled to a temperature approximating that of the atmosphere, being cooled through the conduit 7.

All such structure as has thus far been enumerated is well known in the art.

It will be observed from Figures 2 to 6 inclusive, that the header 6 is supplied with liqueed refrigerant through a valve 9 controlling the conduit 10 which leads from the condenser.

A float 11 within the header and supported by the body of liquefied refrigerant within said header is pivotally mounted within operative proximity to the steam l2 of the valve 9. The valve preferably opens outwardly and the arm 13 of the float which actuates said valve is preferably provided with a clearance or lag 14, so that the level of liquefied refrigerant within the header 6 may suffer an eX- tensive lowering before the float arm 13 comes in contact with the valve stem 12 for opening said valve. Normally the valve is held closed by the compression pressure which may reach a value of one hundred or one hundred twenty lbs. dependinl upon the temperature of the medium whic surrounds the evaporator. A spring l which surrounds the valve stem 12 assists the compression pressure in holding the valve to its seat. The float is preferably made heavy so that after it contacts with the valve stem 12, further recession of the liquid will cause the weight of the fioat to suddenly open the valve when the weight of the float overcomes the combined pressure of the compressor and the spring 15.

It` is preferred, although not essential that yieldin detent means such for instance, as the lea spring 16 be arranged in the ath of the float arm 13, so that the weight of t e float must first overcome the resistance of said spring and that when the arm 13 has finally overcome said spring it strikes the valve stem 12 with an impact blow sufficient certainly to unseat said valve. The leaf spring 16 also acts as a buffer to prevent a premature actuation of the valve by the fioat as might sometimes occur if the float arm 13 were in contact with the valve stem and that the critical pressure was being approached in response to which the valve would open. At this time, if a/door of the refrigerator were slammed the jar might lift the valve from its seat. The intercallation of the leaf sprin 16 prevents this by positively holding the oat arm 13 out of contact with the valve stem until the pressure of the unsupported float is sufficient to open the valve when the float arm has snapped past the spring.

In ordinary mechanical refrigeration apparatus of the float supplied type the valve usually o ens inwardly with the compression pressure eing closed by the float which in general, is mechanically connected to said valve. In such refrigeratin apparatus the boilin ofthe refrigerant in t e header causes a slig t lowering of the li uid level in the evaporator, depressing the oat a slight distance and openlng the supply valve to a slight degree sufficient to admit enough of the liquefied refrigerant to restore the liquid to its normal level, at which time the float valve closes, and thus the float repeatedly opens and closes the supply valve admitting only a slight amount of liquid refrigerant at each time and never enough at one time to effect defrosting of the evaporating unit.'

n the present invention since the valve opens against compression pressure, a force in excess of the compression pressure must be realized on the header side of the valve in order to cause the opening of the supply valve. In order to obtain such an excess force, the boiling within the header must have continued until the liquid level has reached such a low point that the fioat arm 13 contacts with the valve stem 12. Then the liquefied refrigerant must boil down still further until the liquid level has exposed enough of the float to constitute an unsupported weight suf- I ficient to snap past the leaf spring 16 and open the valve 9 by impact against the valve stem 12.

When the valve 9 has once opened, and the liquefied refrigerant has started to flow through the passage 20 uncovered by the valve, the compression pressure becomes ef: fective on the seat side of the valve to the extent of its uncovered area, thus reducing the closing pressure and the valve remains open until enough liquefied refrigerant has flowed into the header to restore the float to its normal position shown in Figure 5 just as soon as the buoyancy of the float has caused the float arm 12 to overcome the retardation of the spring 16. Since the closing pressure as stated may be as much as one hundred pounds per square inch, and the annulus uncovered by the cracking 0f the valve may be at the rate one-half the area of the head of the valve and therefore subject to a counter-pressure of one-half the pressure on the head, it follows that the float havin acquired an unsupported weight by the boi ing away of the liquid sufficient to open the valve against the one hundred pounds per square inch, now finds itself resisted by a pressure of only one-half of this amount and therefore it falls to the bottom of the header, opening the valve wide, the liquid fiowing in meanwhile and raising the level to the former buoyancy level of the float before the inertia of the fioat has permitted the float to gain enough impetus to rise sufficiently to part company with the valve stem so as to cut off' the inflow of theV liquid refrigerant. Thus a gap is created and maintained even in the absence of the spring 16, and the particular advantage of the gap where the spring is not present, is to prevent such minute agitationsof the liquid level as might occur through the slamming of a door to open the valve, as might happen if the float were against the valve stem. In this filling operation a body of liquefied refrigerant has been admitted to the header 6 at one time, which is a very appreciable portion of its normal capacity, equal probably to one- Y half the contents of the header, and this body of liquefied refrigerant has come from a point in the circulation system between the condenser and evaporator at which the temperature of the liquefied refrigerant while not as hot as it would be if taken directly from the compressor, is still at about the ordinary atmospheric temperature and therefore, warm compared with the temperature of the walls of the header. i

Consequently, the admission of this relatively large amount of relative warm liquid within the header raises the temperature of the walls thereof sufficiently to cause a .complete melting of the slight film of frost which may be collected upon the header of the evaporator since the last defrosting operation.

It will be understood that while the filling of the evaporator with liquefied refrigerant takes place only after an approximately exhaustive ebullition of the contents of said header and is replenished all at once, the filling periods will be sufficiently frequent, for example, say, once every hour, to avoid formation of more than a slight film of frost onv the header and coils which slight film is practically instantly removed by the slightly warm incoming refrigerant.. l

In mechanical refrigeration apparatus of usual construction, in which the liquefied refri rant is admitted at frequent intervals an in very small quantities, there is never any defrosting of the evaporator resulting from the incoming liquefied refrigerant and consequentl the refrigerator must at times be opened or an hour ortwo to the atmosphere in order that the frost may melt from the coils by atmospheric temperature. A

This procedure of course, places the refrigerator out of commission as a cooling device for Whatever interval of time is required to effect defrostin and this is absolutely fatal to the use o such a refrigerator for the preservation of foods which have been frozen by the new nick-freezing process and which must never e exposed to a temperature above freezing. In those refrigerators which it is necessary to defrost by opening the refrigerator doors, it is practical to defrost only once every two or three days or perhaps once a week. Cons uently, in this time the frost has accumu ated to great thickness upon the evaporator elements, seriously impairing the heat exchanging efficiency of the evaporator walls and thus lowering the efficiency of the refrigerator. Furthermore, the moisture involved in the frosting represents so much moisture dehydrated from the foods in the refrigerator. By the present invention defrosting takes place regy, ularly and automatically every hour or so,

not much frost has a chance to accumulate, returning moisture. to the atmosphere of the refrigerator at frequent intervals so that the abstraction of moisture from the atmosphere is not cumulative and therefore dehydration of the foods is minimized.

Figure shows a chamber 21 surrounding the valve casing 22 and communicating with the annular passage by means of a plurality of bores 23. The chamber 21 communicates with the interior of the header 6 by means of a narrow annular space 24. The evaporator coils 25, which surround the ice tra-y or freezing chamber 26 preferably communicate at one end as shown at 27 in Figure 5 with the chamber 21, and at the other end they communicate direct with the'header 6 as indicated at 28. In small household units i in which the evaporator coils do not extend for a'great distance below the header 6, a special means for defrostin these coils may be i ored, and the entire body of liquefied refri erant admitted during the the fillin perio to the header 6. The conductivity o the headel walls and the walls of the freezing coils which areV preferably made of copper, is sufficient to conduct the heat of the replenishment charge almost instantly to the lower-most parts of the coils effecting their defrosting. In larger units and particof the refrigerator at the front end as s own,

and discharges at the rear end, it is to be understood that in the normal functioning of the evaporator the liquid refrigerant in the coolin coils boils at all points and conseuentl t eevaporating gaseous refrigerant ows rom said coils at both ends into the header.v In that form of the invention in which the filling charge of liquefied refriger ant is directed through the coils, it is tobe understood that a part of said charge will at the same time be admitted directly to the header through the annular passage 24 or its equivalent.

In order to prevent frosting between the valve stem and valve casing the valve stem is made with a close sliding fit and the bores 23 relieve any tendency of the refrigerant under pressure to bleed by the valve and valve stem.

` Figures 5 and 6 illustrate a valve assembly which can be serviced entirely from outside the header. In order to replace the valve,

it is necessary merely to disconnect the conduit 10, draw off the liquefied refrigerant from the header in known manner, and to remove the valve assembly consisting of the casing 22, valve 9 with its stem 12 and the spring 15. These may be instantly replaced by a new assembly, the same being screwed in against a suitable gasket 29, preferably of lead. It is only necessary then to re-connect the conduit 10 and to re-introduce the liquefied refrigerant into the evaporator.

In'order to preserve a good Valve seat and to prevent particles of foreign substance from lodging between the valve and its seat it may be advantageous to give the valve a slight rotary motion as it leaves and approaches its seat. This may be accomplished by forming the valve stem 12 with a steeply inclined slot as shown in Figure 1l, with a pin 31 projecting from the valve casing 22 into said slot.

Since the pressure of the compressor sometimes builds up to an excessive value as for instance, in hot weather when the refrigerator is kept in a particularly hot place, the valve opening mechanism should have sufcient reserve force to assure the opening of the valve under all conditions of compression pressure. This force is easily realized by having the valve stem struck an impact blow at the instant of opening, since an impact pressure greatly exceeds any gradual pressure which may be effected by the same force. This impact is taken care of in that form of the invention shown in Figure 5, as has been stated, by the spring 16 which suddenly yields to superior float pressure and permits the float arm 13 to rest against the valve stem, but this impact pressure may be produced in many other ways, any of which may be regarded as `equivalents in their application to the present invention.

One of the alternative means for producing the impact blow is shown in Figures 8, 9 and 10 in which a pair of cooperating fioats 32 and 33 are shown within the header 6 and having a common pivotal connection 34. A spring 35 is maintained in tension between the stems of said floats being adapted to pass over the common pivotal point 34 as the float stems deviate from a straight angle. This construction is known as a snap actuated float and is old in the art.

lVhen the liquid level in the header` recedes the floats 32 and 33 descend, the float stems approach one another angularly and the spring gradually contracts below the pivotal point 34. The fioat stems are formed as bell cranks carrying interdigitating cam fingers 35 and 36 which cooperatively embrace one end of a bell crank lever 37. The other end of said lever presses a valve 38 into closed position with respect to the supply of liquefied refrigerant under pressure. As the floats descend the cam fingers permit the valve 38 to open against the pressure of the refrigerantin the supply conduit. When the liquid llevel in the header 6 has risen to a point at which the spring 35 passes above the pivotal connection 34, the spring suddenly contracts, raising the floats under spring pressure and bringing the cam fingers into impactive engagement with the bell crank 37, suddenly forcing the Valve 38 to its seat.

The same type of snap float is equally adaptable for use in imparting an impactive opening movement to a valve similar to that shown in Figure 5, as will be seen from Figure 10, dotted line position and Figure 12. In these figures the arrangementof floats and springs are the same as has been described with respect to the showing in Figures 8, 9

and the full line showing of Figure 10. The

cam fingers 35 and 36 in this instance however, are placed beneath the normal level of the floats and act impactively against the upper side of the bell crank lever 37 as the floats descend and the spring 37 snaps beneath the fulcral point 34 of the float stems. This causes the bell crank lever 37 to impart a hammer blow to the valve stem 12.

Referring once again to Figures 5, 6, and 7, novel means is shown for producing a critical separation of the oil layer from the liquid refrigerant in the header 6 and for returning the same to the compressor. It is well known to be practically impossible to prevent the lubricating oil from the compressor getting by the piston rings and being forced with the liquefied refrigerant into the header. The oil being of less specific gravity than the refrigerant floats on the top in a layer or film of varying depth, depending upon the mechanical condition of the compressor and otherfactors.

The presence of oil inthe evaporator has at least two distinct disadvantages; in the first place, it is not in the compressor where it should be and consequently, the compressor suffers from dearth of lubrication. Secondly, the layer of oil inhibits ebullition from the surface of the body of refrigerant in the evaporator by acting as heat insulation therefor, and consequently lowers the efliciency of the apparatus.

It is old to attempt to draw off this oil through the suction pipe which leads from the evaporator, by means of a small bore tube communicating with said suction pipe and having its end dipping beneath said oil layer and located at a point supposed to be in the plane of the surface of the body of liquefied refrigerant. Such tubes in the prior art have been fixed with respect to the header. It happens however, that in practice the high level of liquefied refrigerant does not always stay in the same place. For instance, due to long service the pivotal connections by which the float is mounted may wear loose. In some systems there are several links between the float and the element immediately concerned in the actuation of the valve and the looseness at these connections is cumulative. The result is that the float tends to stand at a higher level and the liquid level rises accordingly so that as the mouth of the oil drain tube is fixed with respect to the original high liquid level, it dips below the surface of the body of liquefied refrigerant under the conditions of wear above described. Consequently, not only is the oil drawn into the suction pipe but a certain amount of the liquefied refrigerant as well. This results in ordinary apparatus in a continual lowering of the liquid level in the evaporator irrespective of its boiling rate and causes the supply valve to be Vopened continually thus materially reducing the efficiency of the refrigcrating apparatus. Furthermore, the drawing of the liquefied refrigerant into the suction tube l causes frosting of the latter on the inside, materially reducing its effective cross section and preventing the gaseous refrigerant being drawn awa as fast as it is generated. This tends to build up pressure in the header'and reduces the rapidity of evaporation and consequently, lowers the refrigerating efficiency of the machine.

The present invention maintains the mouth of the oil drain pipe at the level of the surface of the liquid refrigerant regardless of the height of this level.

Figure 5 shows an oil drain tube 39 which instead of being fixed relative to the header as is usual, lis pivotally mounted on said header. Figure 7 shows that the end wall 40 of the header is provided with a boss 41 having a transverse bore 42, the. walls of which act as a bearing for a transversely disposed portion 43 of the oil drain tube' the latter being freely oscillatable within said bearing. In the exemplary illustration of the device, the free end of the transversely disposed portion 43 is plugged as shown at 44, although it is obvious that it may be closed in any other suitable manner. The rearward wall of the said transversely disposed portion of the drain tube in that part which intersects the suction pipe 7 is apertured as shown at 45 so that the suction of the compressor is shared in part by the oil drain tube as well as by the free end of the suction pipe.

The opposite end or mouth 46 of the oil drain tube is loosely retained between pins 47 and 48, or equivalent devices attached to the float and these pins are so located that the lower edge of the oil drain tube just touches the surface of the body of liquid refrigerant. Since the oil drain tube is mounted to oscillate in a vertical plane, and the free end is supported by the float- `at a particular position with respect to said float, it is obvious that as the float rises or level of the body of liquid refrigerant, the oil drain pipe will likewise shift its position so as to maintain the lower edge of its mouth always at the surface of the body of liquid refrigerant. It will be seen from Figures 5, 6 and 7 that the mouth of the oil drainjube is always remote from any of the walls of the evaporator and therefore, at the most quiescent region in the surface of the body of refrigerant so that practically none of the liquid refrigerant will ever be splashed into the oil drain tube through ebullition.

While I have in the above description endeavored to disclose preferred and practical embodiments of the invention, it is to be understood that the details of construction as shown are to be considered by way of example only, and not as limitative in their bearing upon the scope of the invention as claimed.

What I claim is:

falls due to change in thel 1. In refrigeration apparatus operating through a Carnot' refrigeration cycle, an evaporator, and means responsive to depletion of refrigerant in said evaporator for periodically introducing into said evaporator a quantity of liquefied refrigerant at one time, sufficient to melt frost from said evaporator.

2. In refrigeration apparatus operating through a Carnot refrigeration cycle, an evaporator, a condenser, and means responsive to depletion of refrigerant in said evaporator for periodicall introducing into said evaporator from sai condenser a quantity of liquefied refrigerant at one time, sufficient to melt frost from said evaporator.

3. In refrigeration apparatus operating through a Carnot refrigeration cycle, an evaporator, a valve for introducing liquefied refrigerant into said evaporator, and impact means operating responsive to a predetermined drop in the liquid level in said evaporator for opening said valve.

4. In refrigeration apparatus operating through a Carnot refrigeration cycle, and an evaporator, a valve for introducing liquefied refrigerant into said evaporator, and impact means for opening said valve, said impact means being so adjusted as to operate responsively only7 to such a predetermined drop in the level of the lliquefied refrigerant in said evaporator as to ensure the replenishment of said evaporator with a. quantity of liqueed refrigerant at one time suicient to melt frost from said evaporator.

5. In refrigeration apparatus as claimed in claim 4, the Carnot c cle including a condenser and the lique ed refrigerant being supplied to` said evaporator from said condenser. y

6. In refrigeration apparatus operating through a Carnot refrigeration cycle, an evaporator including a header, a conduit supplying liquefied refrigerant to said header under pressure of the compressor, a valve controlling communication between said conduit and header, a float including actuating mechanism for said valve means providing a gap in said valve actuating mechanism, and a detent engageable with said iioat controlled valve actuating mechanism on the ioat side of said gap, constructed to preserve the gap and delay the descent of said float and its subsequent return to valve closing position until said float has realized a pressure sutlicient to open said valve by impact, and hold it open by inertia of said oat until a quantity of liquid suicient to restore the float to its normal level and which is sutlicient to melt frost from said evaporator has been admitted to said evaporator.

7. In refrigeration apparatus operating through a Carnot refrigeration cycle, an `evaporator including a header, and a refrigerating tube having its ends communicating with said header at remote points, a conduit on the pressure side of said compressor supplying liquefied refrigerant both to said `neader direct and to said refrigerating tube a valve in said supply conduit opening against the compression pressure having a head exposed to the compression pressure and a. seating surface on the opposite side of said head exposed to counter-pressure upon initial opening of said valve, a ioat in said header responsive to changes in the level of the body of liquid refrigerant in said header for actuating said valve whereby upon a predetermined drop in the level of said liquid refrigerant in said header, a quantit of liquefied refrigerant sufficient tovr melt rOst from said evaporator is supplied to said header boi direct and by Way of said refrigerating tu 8. In refrigeration apparatus operating through a Carnot refrigeration cycle, an evaporator including a header and a freezing tube having its ends connected at remote points to said header, and means for periodically introducing into said evaporator a quantity of liquefied refrigerant at one time sufficient to melt frost from said evaporator, including a valve casing forming with said header a chamber, with which one end of said freezing tube communicates a conduit communicating with said casing for supplying liquefied refrigerant under pressure of the compressor to said header direct, and to said chamber, a valve slidable in said casing having a head exposed to the compression pressure and a seating surface on the opposite side of said head exposed to counter-pressureY upon the initial opening of said valve controlling communication of said conduit with said header and chamber, said valve and casing being removable as a unit exteriorly from said header.

9. In refrigeration apparatus operating through a Carnot refrigeration cycle, and an evaporator including a header, a float in said header including valve actuating mechanism for determining the level of the surface of the body of liquefied refrigerant in said header, and for determining the replenishment periods thereof, a suction pipe, and an oil return tube pivotally mounted and communicating with said suction` pipe having its outer end carried by said float and at the level of the surface of the body of liquefied refrigerant in said header.

10. In refrigeration apparatus as claimed I in claim 9, the oil return tube opening at the surface of the body of. liquefied refrigerant at a point remote from the walls of the header and therefore in the most quiescent region of said surface. I

` In testimony whereof I aiiiX my signature.

HAROLD H. NESBITT. l 

